With Rafael Nadal's future clouded by constant injury troubles, world number one Novak Djokovic stands firmly in the way of Federer and his 18th Grand Slam title.

Though 33-year-old Federer has beaten Djokovic recently, his last win against Serb in a Grand Slam came in 2012 Wimbledon final.

"It gets tougher from here but I still think Roger can win a Grand Slam," Ivanisevic said.

"He can also beat Novak in a major but if it goes down to the fifth set, Novak has a better chance because he is physically better. At the same time, Federer can wrap up the match in three or four sets. Federer is Federer.

"As soon he steps on the court, he is ready, he is tough and nobody can underestimate him. He played great last year though he did not win a Grand Slam. This year as well he has been good and it is going to an interesting season," said the Croatian.